JPH06218254A - Composite film and performance-recovering method therefor - Google Patents

Abstract

PURPOSE:To obtain a compsite film having sufficient durability against wide concentration range of various organic materials and high permeation rate and separation factor by applying a specific copolymer on at least one side of the surface layer of a porous film. CONSTITUTION:The composite film is obtained by applying the copolymer composed of vinyl chloride, vinyl acetate and vinyl alcohol or the copolymer composed of vinyl chloride, vinyl acetate and maleic acid on at least one side of the surface layer of the porous film. By using the composite film, precise separation at a high and stable separation factor and large permeation rate in industry for long term use is provided. And the film is adaptable in wide application such as vapor permeation, dialysis and dehumidifying of air by making use of the characteristics.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a composite membrane suitable for the purpose of separating a water / organic mixed liquid or an organic / organic mixed liquid by pervaporation, vapor permeation or permeation extraction, and a method for recovering the performance thereof. Regarding

[0002]

2. Description of the Related Art Regarding the concentration and separation of an aqueous organic solution using a membrane, a reverse osmosis method has been put into practical use for the concentration of some low-concentration aqueous organic solutions. However, the reverse osmosis method cannot be applied to a high-concentration aqueous solution having a high osmotic pressure because it is necessary to apply a pressure equal to or higher than the osmotic pressure of the separated solution to the liquid to be separated. Is limited.

On the other hand, permeation vaporization and vapor permeation are in the spotlight as separation methods which are not affected by osmotic pressure. The pervaporation method is a method in which the liquid to be separated is supplied to the primary side of the membrane and the secondary side (permeation side) of the membrane is depressurized or a carrier gas is aerated to allow the separated substance to permeate through the membrane in a gaseous state. The method is different from the vapor permeation method in that the supply to the primary side of the membrane is a mixed vapor, which is different from the pervaporation method. The membrane-permeable substance can be collected by cooling and concentrating the permeated vapor.

Many studies have been reported so far regarding the pervaporation method. For example, US Pat.
U.S. Pat. No. 4,067,805 and U.S. Pat. No. 4,067,805 have examples of separation of water / organic mixed liquids by polymers having active anionic groups. U.S. Pat. No. 2953502 and U.S. Pat. There is an example of separation of the water / ethanol mixed liquid used. Further, in Japan, in JP-A-59-109204,
There are examples of a cellulose acetate membrane and a polyvinyl alcohol membrane, and a polyethyleneimine crosslinked membrane in JP-A-59-55305. In addition, Japanese Patent Publications No. 54-10548 and 54-
No. 10549 and No. 59-49041 disclose experimental examples in which a water / organic mixed liquid is separated by using a synthetic polymer membrane into which an ionic group is introduced. However, it can be said that the separation performance exhibited by the membranes described in these publications is particularly low in permeation rate and poor in practicality.

Further, based on the theory that the permeation of liquids and vapors is governed by dissolution and diffusion, attempts have been made to separate by the size difference of permeation molecules using a membrane with a small free volume. (J. Memb. Sci., 30, 1987).
However, the membrane having a small free volume has a drawback that the separation coefficient is large but the permeation rate is small. For this reason, there have been attempts to utilize the difference in the solubility of substances in order to increase the permeation rate and further increase the selectivity. For example, Japanese Patent Application Laid-Open No. 56-24007 discloses a permeable membrane in which a water permeation rate is improved by introducing a sulfone group into the molecular chain of an aromatic polyamideimide. As the number increased, the membrane-forming ability became poor, and the mechanical strength of the obtained membrane decreased, and the selectivity due to molecular size was lost due to swelling, resulting in the loss of the separation selectivity between water and organic matter. .

Therefore, in order to increase the permeation rate of these films, a thinning technique such as coating is required for practical use, but it was difficult to put them into practical use due to the problem of cracking of the coat layer.

[0007]

DISCLOSURE OF THE INVENTION It is an object of the present invention to separate organic / organic mixed liquids or water / organic mixed liquids by pervaporation, vapor permeation or permeation extraction over a wide concentration range of various organics. It is intended to obtain a composite membrane having sufficient durability, a high permeation rate and a separation coefficient, and to provide a method for recovering the membrane performance when a crack occurs in a coat layer.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, in the present invention, a copolymer composed of vinyl chloride, vinyl acetate and vinyl alcohol or a copolymer composed of vinyl chloride, vinyl acetate and maleic acid is provided on at least one surface layer portion of the porous membrane. Coated composite membrane. Further, in the present invention, the composite film having cracks in the coat layer and defects caused by scratches is heated to a temperature not lower than the glass transition point of the coat layer material copolymer in either a dry or wet environment. The invention relates to a method for recovering the performance of a composite membrane, which is characterized by recovering the membrane performance.

The polymer for the coat layer in the present invention is characterized by being a terpolymer of vinyl chloride, vinyl acetate and vinyl alcohol or maleic acid. Since the permeation rate of water molecules is too slow and the water selectivity is low, a membrane with sufficient separation performance (separation coefficient) cannot be obtained. This separation performance can be improved to some extent by copolymerizing any one of vinyl acetate, vinyl alcohol and maleic acid, but it is difficult to increase the permeation rate. Further, a copolymer of vinyl acetate and vinyl alcohol or maleic acid has low solvent resistance, and a film that can be practically used cannot be obtained. Therefore, it is preferable to copolymerize vinyl chloride, vinyl acetate and vinyl alcohol or maleic acid in order to obtain a membrane having a high separation coefficient and a high permeation rate and solvent resistance.

In this case, vinyl chloride used in the present invention,
The copolymer consisting of vinyl acetate and vinyl alcohol is
The composition ratio thereof is preferably in the range of 2 to 95% by weight of vinyl chloride, 1 to 97% by weight of vinyl acetate, and 1 to 97% by weight of vinyl alcohol. Further, the copolymer composed of vinyl chloride, vinyl acetate and maleic acid has a composition ratio of 2 to 95% by weight of vinyl chloride, 1 to 95% by weight of vinyl acetate, and 1 to 20% by weight of maleic acid. Is preferred.

The method of polymerizing the copolymer is not particularly limited, and it can be produced by a known polymerization method such as suspension polymerization using azobisisobutyronitrile as an initiator in an autoclave. The vinyl alcohol contained in includes that it is obtained by partial saponification of vinyl acetate, and similarly, the maleic acid in the copolymer is obtained by copolymerizing maleic anhydride and then hydrolyzing it. It is also.

These copolymers have a weight average molecular weight of 1,000 to 500,00 in terms of polystyrene-converted molecular weight range determined by gel permeation chromatography.
It is preferably in the range of 0, and further 20,000 to 40,000
It is desirable that it be in the range of 3 to express good separation performance.

In the production of the composite membrane of the present invention, various materials such as an ultrafiltration membrane, a reverse osmosis membrane, and a polymer separator sheet used in a battery can be used as the porous membrane used as the support membrane. Although it is possible, the nitrogen gas permeation rate Q (N ₂ ) of the membrane is at least 5 × 10 ⁻⁶ cm ³ (STP) / cm ² because it does not become the resistance of the molecule that permeates the membrane.
・ It must be sec / cmHg or more. Where STP
Means a standard state (Standard Temp. Press.) At 0 ° C. and 1 atmosphere.

In coating, these copolymers are dissolved at a concentration of 1 to 20% by weight in an organic solvent which is a non-solvent with respect to the porous material used for the supporting film, and applied on the porous material. After that, heating is performed in a dry or wet manner to remove the solvent. At this time, heating to a temperature equal to or higher than the glass transition point of the applied copolymer causes the coat layer to adhere to the porous body and the copolymer molecule. It is desirable for chain annealing. The thickness of the coat layer is suitably 10 μm or less.

Further, in general, the composite film is liable to crack in the coat layer, which causes a problem of performance deterioration, but the copolymer used in the coat layer of the composite film according to the present invention is not crosslinked. Since the polymer becomes rubbery at a temperature above the glass transition point, it is possible to repair the cracks that have occurred. Therefore, the separation membrane with cracks in the coat layer should be a water / organic mixed liquid or an organic / organic mixed liquid to be separated, or instead of the supplied liquid, water or polyethylene glycol having an average molecular weight of 600 or less. of,
Add another liquid that does not attack the membrane and heat it to a temperature above the glass transition temperature (wet type), or if that is not possible, remove the supply liquid and bring the membrane to a temperature above the glass transition temperature. The performance can be recovered by heating (dry type).

The composite membrane thus produced is separated from a general solvent such as ethanol, isopropanol, hexane, cyclohexane or diethyl ether by using separation means such as pervaporation method, vapor permeation method and permeation extraction method. It can be applied to dehydration and demethanol removal from dimethyl carbonate / methanol azeotrope.

[0018]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

Here, the separation coefficient (α) is obtained from the following equation. α = (X _p / Y _p ) / (X _f / Y _f ), where X and Y are the weight compositions of water and organic substances in the binary system, and p and f are the permeation side of the membrane and Represents the supply side.

Example 1 In an autoclave, water in which a small amount of polyvinyl alcohol having a hydrolysis rate of 80% was dissolved, an initiator azobisisobutyronitrile and a vinyl acetate monomer were added, and the lid was closed. The autoclave was cooled to -20 ° C in a methanol bath. Similarly, the vinyl chloride monomer liquefied by cooling was charged into an autoclave, and the temperature was raised to 58 ° C. with stirring to carry out polymerization. The polymerization reaction was stopped when the pressure started to decrease, and the resulting polymer was washed with water and dried. A polyacrylonitrile-based asymmetric ultrafiltration membrane, DUY-L flat membrane (manufactured by Daicel Chemical Industries, Ltd.) was washed with water and then air-dried, and the copolymer previously polymerized on this membrane (weight average molecular weight 40,000, vinyl chloride / A 5 wt% tetrahydrofuran solution of vinyl acetate / vinyl alcohol = 80/5/15 (wt%), glass transition point 72 ° C.) was coated. Next, this film was dried at 85 ° C. under normal pressure for 1 hour to form a composite film (coat layer thickness 4 μm). The dewatering performance (evaluation liquid 90% by weight isopropanol, 70 ° C) from water / isopropanol mixture was measured at 5 mmHg by the pervaporation method.
(α) = 1,000 and permeation rate = 0.81 kg / m ² · hr were obtained.

Example 2 Water in which a small amount of polyvinyl alcohol having a hydrolysis rate of 80% was dissolved, an initiator azobisisobutyronitrile, a vinyl acetate monomer and maleic acid were added to an autoclave, and the lid was closed. The autoclave was cooled to -20 ° C in a dry ice / methanol bath. Similarly, the vinyl chloride monomer liquefied by cooling was charged into an autoclave, and the temperature was raised to 58 ° C. with stirring to carry out polymerization. The polymerization reaction was stopped when the pressure started to decrease, and the resulting polymer was washed with water and dried.

DUY-L flat membrane (manufactured by Daicel Chemical Industries, Ltd.), which is a polyacrylonitrile-based asymmetric ultrafiltration membrane, was washed with water and then air-dried, and the copolymer previously polymerized on this membrane (weight average molecular weight 30,000, A 5 wt% tetrahydrofuran solution of vinyl chloride / vinyl acetate / maleic acid = 81/17/2 (wt%), glass transition point 75.0 ° C.) was coated. Next, this film was dried at 85 ° C. for 1 hour under normal pressure to form a composite film (coat layer thickness 5 μm). The dewatering performance (evaluation liquid 90% by weight isopropanol, 70 ° C) from water / isopropanol mixture was measured at 5 mmHg by the pervaporation method.
(α) = 1,600 and permeation rate = 0.55 kg / m ² · hr were obtained.

Comparative Example 1 DUY-L, which is a polyacrylonitrile-based asymmetric ultrafiltration membrane
A flat membrane (manufactured by Daicel Chemical Industries, Ltd.) was washed with water and air-dried, and a 5 wt% tetrahydrofuran solution of polyvinyl chloride having a weight average molecular weight of 50,000 was coated on the membrane. Next, this membrane was dried at 85 ° C. under normal pressure for 1 hour to obtain a composite membrane.
(Coat layer thickness 5 μm). The dehydration performance (evaluation liquid 90 wt% isopropanol, 70 ° C) from water / isopropanol mixture was measured at 5 mmHg by the pervaporation method. As a result, the separation coefficient (α) = 137 and the permeation rate = 0.06 kg / m ² · hr Obtained.

Comparative Example 2 DUY-L, which is a polyacrylonitrile-based asymmetric ultrafiltration membrane
A flat membrane (manufactured by Daicel Chemical Industries, Ltd.) was washed with water and air-dried, and a vinyl chloride / vinyl acetate copolymer having a weight average molecular weight of 30,000 (90% by weight vinyl chloride, 10% vinyl acetate) was formed on the membrane.
Wt%) in a 5 wt% tetrahydrofuran solution. Next, this film was dried at 85 ° C. for 1 hour under normal pressure to form a composite film (coat layer thickness 5 μm). As a result of measuring the dehydration performance (evaluation liquid 90% by weight isopropanol, 70 ° C) at 5 mmHg from the water / isopropanol mixture by pervaporation, the separation coefficient (α) = 1,020, permeation rate = 0.09 kg / m ² ·
got hr.

Example 3 The composite membrane (α = 1,000, permeation rate = 0.81 kg / m ² · hr) prepared and evaluated in the same manner as in Example 1 had a permeation side pressure of 5 mmHg to normal pressure. The pressure was rapidly released to (5 mmHg to normal pressure for 3 seconds). As a result, the coat layer cracks,
The membrane performance was α = 495 and the permeation rate = 0.93 kg / m ² · hr even after the permeation side was decompressed again (8 mmHg). In this state, the temperature of the supply liquid was raised from 70 ° C to 83 ° C and maintained at this temperature for 1 hour. Thereafter, when the temperature of the supply liquid was returned to 70 ° C. again and the membrane performance was measured, the separation coefficient (α) was 2,500 and the permeation rate was 0.80 kg / m ² · hr.

Example 4 The composite membrane (α = 1,600, permeation rate = 0.55 kg / m ² · hr) prepared and evaluated in the same manner as in Example 2 had a permeation side pressure of 5 mmHg to normal pressure. The pressure was rapidly released to (5 mmHg to normal pressure for 3 seconds). As a result, the coat layer cracks,
The membrane performance was α = 9 and the permeation rate = 1.51 kg / m ² · hr even after the permeation side was evacuated again (15 mmHg). The film was removed from the evaluation cell, heated at 85 ° C under normal pressure for 1 hour, and then set in the same cell again to measure the performance.
The separation coefficient (α) was 2,200 and the permeation rate was 0.50 kg / m ² · hr.

Comparative Example 3 A composite membrane (α = 1,000, permeation rate = 0.81 kg / m ² · hr) prepared by the same method as in Example 1 and evaluated for performance had a permeation side pressure of 5 mmHg to normal pressure. The pressure was rapidly released to (5 mmHg to normal pressure for 3 seconds). As a result, the coat layer cracks,
Even after the permeation side was decompressed again (8 mmHg), the membrane performance was α = 432 and the permeation rate = 0.95 kg / m ² · hr. In this state, the supply temperature of 70 ° C. was maintained for 1 hour. After that, when the membrane performance was measured, the separation coefficient (α) = 440, the permeation rate = 0.9
It was 5 kg / m ² · hr.

[0028]

By using the composite membrane of the present invention,
In the industrial long-term use, it is possible to provide a highly stable separation coefficient and a precise separation with a large permeation rate. Further, by utilizing the characteristics of the membrane according to the present invention, it can be applied to a wide range of applications such as vapor permeation, dialysis and dehumidification of air.

Claims (5)

[Claims] 1. A surface layer portion of at least one of the porous membranes,
A composite film coated with a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, or a copolymer of vinyl chloride, vinyl acetate and maleic acid. 2. The composition ratio of the copolymer composed of vinyl chloride, vinyl acetate and vinyl alcohol is from 2 to 2 vinyl chloride.
The composite membrane according to claim 1, wherein the weight average molecular weight of the copolymer is in the range of 1,000 to 500,000, and the weight average molecular weight of the copolymer is in the range of 95% by weight, 1 to 97% by weight of vinyl acetate and 1 to 97% by weight of vinyl alcohol. 3. The composition ratio of the copolymer composed of vinyl chloride, vinyl acetate and maleic acid is such that vinyl chloride is 2 to 95% by weight, vinyl acetate is 1 to 95% by weight, and maleic acid is 1 to 20% by weight.
And the weight average molecular weight of the copolymer is 1,0
The composite membrane according to claim 1, which is in the range of 00 to 500,000. 4. The composite membrane according to claim 1, which is for pervaporation separation, vapor permeation separation or permeation extraction. 5. The composite film according to any one of claims 1 to 3 in which defects such as cracks and scratches have occurred in the coat layer, which are used as a coat layer material in either a dry or wet environment. A method for recovering the performance of a composite film, comprising recovering the film performance by heating to a temperature not lower than the glass transition point of the polymer.